Metal-dielectric optical filter, sensor device, and fabrication method

ABSTRACT

An optical filter, a sensor device including the optical filter, and a method of fabricating the optical filter are provided. The optical filter includes one or more dielectric layers and one or more metal layers stacked in alternation. The metal layers are intrinsically protected by the dielectric layers. In particular, the metal layers have tapered edges that are protectively covered by one or more of the dielectric layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/266,913, filed Feb. 4, 2019, which is a continuation of U.S. patentapplication Ser. No. 14/308,343, filed Jun. 18, 2014 (now U.S. Pat. No.10,197,716), which is a continuation-in-part of U.S. patent applicationSer. No. 13/720,728, filed Off Dec. 19, 2012 (now U.S. Pat. No.9,448,346), which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a metal-dielectric optical filter, asensor device including such an optical filter, and a method offabricating such an optical filter.

BACKGROUND OF THE INVENTION

Optical sensors are used in optical sensor devices, such as imagesensors, ambient light sensors, proximity sensors, hue sensors, and UVsensors, to convert optical signals into electrical signals, allowingdetection of optical signals or image capture. An optical sensor,generally, includes one or more sensor elements and one or more opticalfilters disposed over the one or more sensor elements.

For example, a color image sensor includes a plurality of color filtersdisposed in an array, i.e., a color filter array (CFA). The CFA includesdifferent types of color filters having different color passbands, e.g.,red, green, and blue (RGB) filters.

Conventionally, absorption filters formed using dyes are used as colorfilters. Unfortunately, such dye-based color filters have relativelybroad color passbands, resulting in less brilliant colors.Alternatively, dichroic filters, i.e., interference filters, formed ofstacked dielectric layers may be used as color filters. Suchall-dielectric color filters have higher transmission levels andnarrower color passbands, resulting in brighter and more brilliantcolors. However, the color passbands of all-dielectric color filtersundergo relatively large center-wavelength shifts with changes inincidence angle, resulting in undesirable shifts in color.

Furthermore, all-dielectric color filters, typically, include a largenumber of stacked dielectric layers and are relatively thick.Consequently, all-dielectric color filters are expensive and difficultto manufacture. In particular, all-dielectric color filters aredifficult to etch chemically. Lift-off processes are, therefore,preferred for patterning. Examples of lift-off processes for patterningall-dielectric color filters in CFAs are disclosed in U.S. Pat. No.5,120,622 to Hanrahan, issued on Jun. 9, 1992, in U.S. Pat. No.5,711,889 to Buchsbaum, issued on Jan. 27, 1998, in U.S. Pat. No.6,238,583 to Edlinger, et al., issued on May 29, 2001, in U.S. Pat. No.6,638,668 to Buchsbaum, et al., issued on Oct. 28, 2003, and in U.S.Pat. No. 7,648,808 to Buchsbaum, et al., issued on Jan. 19, 2010, whichare incorporated herein by reference. However, lift-off processes are,generally, limited to a filter spacing of about twice the filter height,which makes it difficult to achieve all-dielectric CFAs suitable forsmaller color image sensors.

In addition to transmitting visible light in color passbands, bothdye-based and all-dielectric color filters also transmit infrared (IR)light, which contributes to noise. Therefore, a color image sensor,typically, also includes an IR-blocking filter disposed over the CFA.IR-blocking filters are also used in other optical sensor devicesoperating in the visible spectral range. Conventionally, absorptionfilters formed of colored glass or dichroic filters formed of stackeddielectric layers are used as IR-blocking filters. Alternatively,induced transmission filters formed of stacked metal and dielectriclayers may be used as IR-blocking filters. Examples of metal-dielectricIR-blocking filters are disclosed in U.S. Pat. No. 5,648,653 toSakamoto, et al., issued on Jul. 15, 1997, and in U.S. Pat. No.7,133,197 to Ockenfuss, et al., issued on Nov. 7, 2006, which areincorporated herein by reference.

To avoid the use of an IR-blocking filter, induced transmission filtersformed of stacked metal and dielectric layers may be used as colorfilters. Metal-dielectric optical filters, such as metal-dielectriccolor filters, are inherently IR-blocking. Typically, metal-dielectriccolor filters have relatively narrow color passbands that do not shiftsignificantly in wavelength with changes in incidence angle.Furthermore, metal-dielectric color filters are, generally, much thinnerthan all-dielectric color filters. Examples of metal-dielectric colorfilters are disclosed in U.S. Pat. No. 4,979,803 to McGuckin, et al.,issued on Dec. 25, 1990, in U.S. Pat. No. 6,031,653 to Wang, issued onFeb. 29, 2000, in U.S. Patent Application No. 2009/0302407 to Gidon, etal., published on Dec. 10, 2009, in U.S. Patent Application No.2011/0204463 to Grand, published on Aug. 25, 2011, and in U.S. PatentApplication No. 2012/0085944 to Gidon, et al., published on Apr. 12,2012, which are incorporated herein by reference.

Typically, the metal layers in metal-dielectric optical filters, such asmetal-dielectric color filters, are silver or aluminum layers, which areenvironmentally unstable and which deteriorate when exposed to evensmall amounts of water or sulfur. Chemically etching the silver layersexposes the edges of the silver layers to the environment, allowingdeterioration. Therefore, in most instances, metal-dielectric colorfilters in CFAs are patterned by adjusting the thicknesses of only thedielectric layers to select different color passbands for themetal-dielectric color filters. In other words, different types ofmetal-dielectric color filters having different color passbands arerequired to have the same number of silver layers as one another and thesame thicknesses of the silver layers as one another. Unfortunately,these requirements severely limit the possible optical designs for themetal-dielectric color filters.

The present invention provides metal-dielectric optical filters that arenot subject to these requirements, which are particularly suitable foruse in image sensors and other sensor devices, such as ambient lightsensors, proximity sensors, hue sensors, and UV sensors.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to an optical filter,disposed on a substrate, comprising: one or more dielectric layers; andone or more metal layers, stacked in alternation with the one or moredielectric layers on the substrate, wherein each of the one or moremetal layers has a tapered edge, at a periphery of the optical filter,that is protectively covered by at least one of the one or moredielectric layers.

The present invention also relates to a sensor device comprising: one ormore sensor elements; and one or more optical filters disposed over theone or more sensor elements, wherein each of the one or more opticalfilters includes: one or more dielectric layers; and one or more metallayers stacked in alternation with the one or more dielectric layers,wherein each of the one or more metal layers has a tapered edge, at aperiphery of the optical filter, that is protectively covered by atleast one or more dielectric layers.

The present invention further relates to a method of fabricating anoptical filter, the method comprising: providing a substrate; applying aphotoresist layer onto the substrate; patterning the photoresist layerto uncover a filter region of the substrate, whereby an overhang isformed in the patterned photoresist layer surrounding the filter region;depositing a multilayer stack, including one or more metal layersstacked in alternation with one or more dielectric layers, onto thepatterned photoresist layer and the filter region of the substrate;removing the patterned photoresist layer and a portion of the multilayerstack on the patterned photoresist layer so that a portion of themultilayer stack remaining on the filter region of the substrate formsthe optical filter, wherein each of the one or more metal layers in theoptical filter has a tapered edge, at a periphery of the optical filter,that is protectively covered by at least one of the one or moredielectric layers in the optical filter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater detail with referenceto the accompanying drawings wherein:

FIG. 1A is a schematic illustration of a cross-section of a firstembodiment of an optical filter;

FIGS. 1B to 1G are schematic illustrations of steps in a method offabricating the optical filter of FIG. 1A;

FIG. 2 is a schematic illustration of a cross-section of a secondembodiment of an optical filter;

FIG. 3 is a schematic illustration of a cross-section of a plurality ofoptical filters;

FIG. 4A is a table of layer numbers, materials, and thicknesses for anexemplary red filter;

FIG. 4B is a table of layer numbers, materials, and thicknesses for anexemplary green filter;

FIG. 4C is a table of layer numbers, materials, and thicknesses for anexemplary blue filter;

FIG. 4D is a table of layer numbers, materials, and thicknesses for anexemplary photopic filter;

FIGS. 5A and 5B are plots of transmission spectra for the exemplary red,green, and blue filters of FIGS. 4A to 4C;

FIG. 5C is a plot of transmission spectra at incidence angles of 0° to60° for the exemplary photopic filter of FIG. 4D;

FIG. 6A is a plot of color gamuts for the exemplary red, green, and blue(RGB) filter set of FIGS. 4A to 4C and for a conventional dye-based RGBfilter set;

FIG. 6B is a plot of color trajectories at incidence angles of 0° to 60°for the exemplary red filter of FIG. 4A and for a conventionalall-dielectric red filter;

FIG. 6C is a plot of a color trajectory at incidence angles of 0° to 60°for the exemplary photopic filter of FIG. 4D;

FIG. 7 is a schematic illustration of a cross-section of a firstembodiment of a sensor device;

FIG. 8 is a schematic illustration of a cross-section of a secondembodiment of a sensor device;

FIGS. 9A and 9B are scanning electron micrographs of a cross-section ofa continuous coating deposited on a patterned photoresist layer and asubstrate;

FIG. 9C is an optical micrograph of a top view of an optical filterformed from the continuous coating of FIGS. 9A and 9B, showing corrosionafter exposure to high humidity and temperature;

FIG. 10 is a scanning electron micrograph of a cross-section of anon-continuous coating deposited on a patterned photoresist layer and asubstrate;

FIGS. 11A and 11B are scanning electron micrographs of a cross-sectionof a non-continuous coating deposited on a patterned photoresist layer,having a thicker bottom release layer and a larger overhang, and asubstrate;

FIG. 12 is a table of layer numbers, materials, and thicknesses forexemplary ultraviolet-A (UVA), ultraviolet-B (UVB), and 220-nm-centeredfilters;

FIG. 13A is a plot of transmission spectra at incidence angles of 0° to60° for the exemplary UVA filter of FIG. 12 ;

FIG. 13B is a plot of transmission spectra at incidence angles of 0° to60° for the exemplary UVB filter of FIG. 12 ;

FIG. 13C is a plot of transmission spectra at incidence angles of 0° to60° for the exemplary 220-nm-centered filter of FIG. 12 ;

FIG. 14 is a plot of transmission spectra at incidence angles of 0° to60° for an exemplary photopic filter;

FIG. 15A is a schematic illustration of a cross-section of a thirdembodiment of a sensor device;

FIG. 15B is a schematic illustration of a top view of the sensor deviceof FIG. 15A;

FIG. 15C is a schematic illustration of a top view of an alternativelayout for the sensor device of FIG. 15A; and

FIG. 16 is a schematic illustration of a top view of a fourth embodimentof a sensor device.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a metal-dielectric optical filter havingprotected metal layers, which is particularly suitable for use in asensor device, such as an image sensor, an ambient light sensor, aproximity sensor, a hue sensor, or an ultraviolet (UV) sensor. Theoptical filter includes one or more dielectric layers and one or moremetal layers stacked in alternation. The metal layers are intrinsicallyprotected by the dielectric layers. In particular, the metal layers havetapered edges that are protectively covered by one or more of thedielectric layers. Accordingly, the metal layers have increasedresistance to environmental degradation, resulting in a moreenvironmentally durable optical filter.

In some embodiments, the one or more dielectric layers and the one ormore metal layers are stacked without any intervening layers. Withreference to FIG. 1A, a first embodiment of the optical filter 100,disposed on a substrate 110, includes three dielectric layers 120 andtwo metal layers 130 stacked in alternation. The metal layers 130 areeach disposed between and adjacent to two dielectric layers 120 and are,thereby, protected from the environment. The dielectric layers 120 andthe metal layers 130 are continuous layers that do not have anymicrostructures formed therein.

The metal layers 130 have tapered edges 131 at a periphery 101 of theoptical filter 100. In other words, the metal layers 130 aresubstantially uniform in thickness throughout a central portion 102 ofthe optical filter 100, but taper off in thickness at the periphery 101of the optical filter 100. The tapered edges 131 extend along the entireperipheries of the metal layers 130 at the periphery 101 of the opticalfilter 100. Likewise, the dielectric layers 120 are substantiallyuniform in thickness throughout the central portion 102 of the opticalfilter 100, but taper off in thickness at the periphery 101 of theoptical filter 100. Accordingly, the central portion 102 of the opticalfilter 100 is substantially uniform in height, whereas the periphery 101of the optical filter 100 is sloped. In other words, the optical filter100 has a substantially flat top and sloped sides. Typically, the sidesof the optical filter 100 are sloped at an angle of less than about 45°from horizontal. Preferably, the sides of the optical filter 100 aresloped at an angle of less than about 20° from horizontal, morepreferably, at an angle of less than about 10° from horizontal.

Advantageously, the tapered edges 131 of the metal layers 130 are notexposed to the environment. Rather, the tapered edges 131 of the metallayers 130 are protectively covered by one or more of the dielectriclayers 120 along the entire peripheries of the metal layers 130. The oneor more dielectric layers 120 suppress environmental degradation, e.g.,corrosion, of the metal layers 130, e.g., by inhibiting the diffusion ofsulfur and water into the metal layers 130. Preferably, the metal layers130 are substantially encapsulated by the dielectric layers 120. Morepreferably, the tapered edges 131 of the metal layers 130 areprotectively covered by adjacent dielectric layers 120, and the metallayers 130 are substantially encapsulated by adjacent dielectric layers120. In some instances, a top dielectric layer 120, i.e., a dielectriclayer 120 at the top of the optical filter 100, protectively covers thetapered edges 131 of all of the metal layers 130 below.

With reference to FIGS. 1B to 1G, the first embodiment of the opticalfilter 100 may be fabricated by a lift-off process. With particularreference to FIG. 1B, in a first step, the substrate 110 is provided.With particular reference to FIG. 1C, in a second step, a photoresistlayer 140 is applied onto the substrate 110. Typically, the photoresistlayer 140 is applied by spin coating or spray coating.

With particular reference to FIG. 1D, in a third step, the photoresistlayer 140 is patterned to uncover a region of the substrate 110 wherethe optical filter 100 is to be disposed, i.e., a filter region. Otherregions of the substrate 110 remain covered by the patterned photoresistlayer 140. Typically, the photoresist layer 140 is patterned by firstexposing a region of the photoresist layer 140 covering the filterregion of the substrate 110 to UV light through a mask, and thendeveloping, i.e., etching, the exposed region of the photoresist layer140 by using a suitable developer or solvent.

The photoresist layer 140 is patterned in such a manner that an overhang141, i.e., an undercut, is formed in the patterned photoresist layer 140surrounding the filter region. Typically, the overhang 141 is formed bychemically modifying, e.g., by using a suitable solvent, a top portionof the photoresist layer 140, so that the top portion develops moreslowly than a bottom portion of the photoresist layer 140.Alternatively, the overhang 141 may be formed by applying a dual-layerphotoresist layer 140, consisting of a top layer that develops moreslowly and a bottom layer that develops more quickly, to the substrate110.

The overhang 141 should be large enough to ensure that the coating,i.e., the multilayer stack 103, subsequently deposited on the patternedphotoresist layer 140 and the substrate 110 is not continuous from thesubstrate 110 to the patterned photoresist layer 140, as shown in FIG.1E. The overhang 141 is, typically, greater than 2 μm, preferably,greater than 4 μm. In general, the coating should not cover the sides ofthe patterned photoresist layer 140.

With reference to FIGS. 9A and 9B, when the coating 903 is continuousover the substrate 910 and the patterned photoresist layer 940, duringsubsequent lift-off of the photoresist layer 940 and the portion of thecoating 903 thereon, the coating 903 is broken at the bottom edges ofthe patterned photoresist layer 940, exposing the edges of the opticalfilter formed from the coating 903, in particular, the edges of themetal layers of the optical filter, to the environment. Unfortunately,the exposed edges are susceptible to environmental attack, e.g., whenexposed to high humidity and temperature, leading to corrosion, as shownin FIG. 9C for a silver-containing optical filter 900.

With reference to FIG. 10 , in an embodiment that provides anon-continuous coating 1003, the photoresist layer has a bilayerstructure, and includes a top layer 1042 and a bottom layer 1043. Thetop layer 1042 is photosensitive and is patternable by selectiveexposure to UV light. The bottom layer 1043 is, generally, notphotosensitive and acts as a release layer. Suitable examples of resistsinclude AZ Electronic Materials nLOF 2020 for the top photosensitivelayer 1042 and Microchem Corp. LOR 10 B for the bottom release layer1043.

When the photoresist layer is developed, the extent of the overhang 1041is controlled by the development time. In FIG. 10 , the development timewas selected to provide an overhang 1041 of about 3 μm. Preferably, thethickness of the bottom release layer 1043 is greater than about 500 nm,and the overhang 1041 is greater than about 2 μm To ensure cleanlift-off, i.e., lift-off without breakage of the deposited coating 1003,the thickness of the coating 1003 should, generally, be less than about70% of the thickness of the bottom release layer 1043. In FIG. 10 , thethickness of the bottom release layer 1043 is about 800 nm, thethickness of the top photosensitive layer 1042 is about 2 μm, and thethickness of the coating is about 500 nm. The sides of the opticalfilter 1000 under the overhang 1041 are sloped at an angle of about 10°.

With reference to FIG. 11 , in some instances, a thicker bottom releaselayer 1143 is used, and a larger overhang 1141 is produced by using alonger development time, e.g., about 80 s to about 100 s for someprocesses. These features improve edge durability by decreasing theslope of the sides of the optical filter 1100 and increasing thethickness of the top dielectric layer 1121 at the periphery of theoptical filter 1100. In FIG. 11 , the development time was selected toprovide an overhang 1141 of about 6 μm. Preferably, the thickness of thebottom release layer 1143 is greater than about 2 μm, and the overhang1141 is greater than about 4 μm. The thickness of the coating layer 1103should, generally, be less than about 30% of the thickness of the bottomrelease layer 1143. In FIG. 11 , the thickness of the bottom releaselayer 1143 is about 2.6 μm, the thickness of the top photosensitivelayer 1142 is about 2 μm, and the thickness of the coating 1103 is about500 nm. The sides of the optical filter 1100 under the overhang 1141 aresloped at an angle of about 5°.

With particular reference to FIG. 1E, in a fourth step, a multilayerstack 103 is deposited as a non-continuous coating onto the patternedphotoresist layer 140 and the filter region of the substrate 110. Aportion of the multilayer stack 103 disposed on the filter region of thesubstrate 110 forms the optical filter 100. The layers of the multilayerstack 103, which correspond to the layers of the optical filter 100, maybe deposited by using a variety of deposition techniques, such as:evaporation, e.g., thermal evaporation, electron-beam evaporation,plasma-assisted evaporation, or reactive-ion evaporation; sputtering,e.g., magnetron sputtering, reactive sputtering, alternating-current(AC) sputtering, direct-current (DC) sputtering, pulsed DC sputtering,or ion-beam sputtering; chemical vapor deposition, e.g., plasma-enhancedchemical vapor deposition; and atomic layer deposition. Moreover,different layers may be deposited by using different depositiontechniques. For example, the metal layers 130 may be deposited bysputtering of a metal target, and the dielectric layers 120 may bedeposited by reactive sputtering of a metal target in the presence ofoxygen.

Because the overhang 141 shadows a periphery of the filter region of thesubstrate 110, the deposited layers taper off in thickness towards theperiphery 101 of the optical filter 100. The overhang 141 generates asoft roll-off of the coating towards the periphery 101 of the opticalfilter 100. When a dielectric layer 120 is deposited onto a metal layer130, the dielectric layer 120 covers not only the top surface of themetal layer 130, but also the tapered edges 131 of the metal layer 130,thereby, protecting the metal layer 130 from the environment. Moreover,the top dielectric layer 120, generally, serves as a protective layerfor the metal layers 130 below. For example, in the embodiment of FIG.11 , a top dielectric layer 1121 having a thickness of about 100 nmextends over and protectively covers the less durable metal layersbelow, in particular, the tapered edges of the metal layers, as shown inFIG. 11A.

With particular reference to FIG. 1F, in a fifth step, a portion of themultilayer stack 103 on the patterned photoresist layer 140 is removed,i.e., lifted off, together with the photoresist layer 140. Typically,the photoresist layer 140 is stripped by using a suitable stripper orsolvent. A portion of the multilayer stack 103 remaining on the filterregion of the substrate 110 forms the optical filter 100. The substrate110 may, for example, be a conventional sensor element.

It should be noted that the lift-off process of FIGS. 1B to 1F may alsobe used to simultaneously form a plurality of optical filters 100 of thesame type, i.e., having the same optical design, on the substrate 110.Moreover, the lift-off process may be repeated to subsequently form oneor more optical filters of a different type, i.e., having a differentoptical design, on the same substrate 110. In some instances, one ormore optical filters that are more environmentally durable may besubsequently formed on the substrate 110 so that they partially overlapwith one or more optical filters 100 that are less environmentallydurable, as explained in further detail hereafter, by using a lift-offprocess or, in some instances, by using a dry or wet etching process.Thereby, an optical filter array may be formed on the substrate 110. Thesubstrate 110 may, for example, be a conventional sensor array.

With particular reference to FIG. 1G, in an optional sixth step, anadditional protective coating 150 is deposited onto the optical filter100. The protective coating 150 may be deposited by using one of thedeposition techniques mentioned heretofore. The protective coating 150covers both the central portion 102 and the periphery 101 of the opticalfilter 100, i.e., all exposed portions of the optical filter 100,thereby, protecting the optical filter 100 from the environment.

In other embodiments, the optical filter includes a plurality ofcorrosion-suppressing layers, disposed between the dielectric layers andthe metal layers, which further protect the metal layers. With referenceto FIG. 2 , a second embodiment of the optical filter 200, disposed on asubstrate 210, is similar to the first embodiment of the optical filter100, but further includes four corrosion-suppressing layers 260 insertedbetween the three dielectric layers 220 and the two metal layers 230.

The metal layers 230 are each disposed between and adjacent to twocorrosion-suppressing layers 260 and are, thereby, further protectedfrom the environment. The corrosion-suppressing layers 260 suppresscorrosion of the metal layers 230, principally during the depositionprocess. In particular, the corrosion-suppressing layers 260 protectportions of the metal layers 230 in the optical path, inhibitingdegradation of the optical properties of the metal layers 230.Preferably, tapered edges 231 of the metal layers 230 are protectivelycovered by adjacent corrosion-suppressing layers 260, as well as bynearest dielectric layers 220. Thus, the metal layers 230 are,preferably, substantially encapsulated by adjacent corrosion-suppressinglayers 260, as well as by nearest dielectric layers 220.

The second embodiment of the optical filter 200 may be fabricated by alift-off process similar to that used to fabricate the first embodimentof the optical filter 100. However, the layers of the multilayer stackdeposited in the fourth step correspond to the layers of the opticalfilter 200. In particular, corrosion-suppressing layers 260 aredeposited before and after each metal layer 230. Advantageously, thecorrosion-suppressing layers 260 suppress corrosion, i.e., oxidation, ofthe metal layers 230 during deposition of the dielectric layers 220. Thecorrosion-suppressing layers 260 are particularly useful when the metallayers 230 contain silver or aluminum. In such embodiments, thecorrosion-suppressing layers 260 suppress the reaction between silver oraluminum from the metal layers 230 and oxygen from the dielectric layers220 to form silver oxide or aluminum oxide.

The corrosion-suppressing layers 260 may be deposited as metal compound,e.g., metal nitride or metal oxide, layers by using one of thedeposition techniques mentioned heretofore, e.g., reactive sputtering.Alternatively, the corrosion-suppressing layers 260 may be formed byfirst depositing suitable metal layers, by using one of the depositiontechniques mentioned heretofore, and subsequently oxidizing the metallayers. Preferably, the corrosion-suppressing layers 260 on top of themetal layers 230 are each formed by first depositing a suitable metallayer, oxidizing the metal layer, and then depositing a metal oxidelayer. For example, these corrosion-suppressing layers 260 may be formedby sputtering of a suitable metal target followed by oxidation, followedby reactive sputtering of a suitable metal target in the presence ofoxygen. Further details of methods of forming corrosion-suppressinglayers are provided hereafter, and are disclosed in U.S. Pat. No.7,133,197.

The optical filter of the present invention may have a variety ofoptical designs. The optical designs of exemplary optical filters willbe described in further detail hereafter. In general, the optical designof the optical filter is optimized for a particular passband byselecting suitable layer numbers, materials, and/or thicknesses.

The optical filter includes at least one metal layer, and at least onedielectric layer. Often, the optical filter includes a plurality ofmetal layers and a plurality of dielectric layers. Typically, theoptical filter includes 2 to 6 metal layers, 3 to 7 dielectric layers,and, optionally, 4 to 12 corrosion-suppressing layers. In general,increasing the number of metal layers provides a passband with steeperedges, but with a lower in-band transmittance.

The first or bottom layer in the optical design, i.e., the first layerdeposited on the substrate, may be a metal layer or a dielectric layer.The last or top layer in the optical design, i.e., the last layerdeposited on the substrate, is usually a dielectric layer. When thebottom layer is a metal layer, the optical filter may consist of n metallayers (M) and n dielectric layers (D) stacked in a sequence of(M/D)_(n), where n≥1. Alternatively, the optical filter may consist of nmetal layers (M), n dielectric layers (D), and 2n corrosion-suppressinglayers (C), stacked in a sequence of (C/M/C/D)_(n), where n≥1. When thebottom layer is a dielectric layer, the optical filter may consist of nmetal layers (M) and n+1 dielectric layers (D) stacked in a sequence ofD(M/D)_(n), where n≥1. Alternatively, the optical filter may consist ofn metal layers (M), n+1 dielectric layers (D), and 2ncorrosion-suppressing layers (C), stacked in a sequence ofD(C/M/C/D)_(n), where n≥1.

The metal layers are each composed of a metal or alloy. In someembodiments, the metal layers are each composed of silver.Alternatively, the metal layers may each be composed of a silver alloy.For example, a silver alloy consisting essentially of about 0.5 wt %gold, about 0.5 wt % tin, and a balance of silver may provide improvedcorrosion resistance. In other embodiments, the metal layers are eachcomposed of aluminum. The choice of metal or alloy depends on theapplication. Silver is usually preferred for optical filters having apassband in the visible spectral region, and aluminum is usuallypreferred for optical filters having a passband in the UV spectralregion, although silver may sometimes be used when the passband iscentered at a wavelength greater than about 350 nm.

Generally, but not necessarily, the metal layers are composed of thesame metal or alloy, but have different thicknesses. Typically, themetal layers each have a physical thickness between about 5 nm and about50 nm, preferably, between about 10 nm and about 35 nm.

The dielectric layers are each composed of a dielectric material that istransparent in the passband of the optical filter.

For optical filters with a passband in the visible spectral region, thedielectric layers are, typically, each composed of a high-indexdielectric material having a refractive index greater than about 1.65 at550 nm that is transparent in the visible spectral region. Suitableexamples of high-index dielectric materials for such filters includetitanium dioxide (TiO₂), zirconium dioxide (ZrO₂), hafnium dioxide(HfO2), niobium pentoxide (Nb₂O₅), tantalum pentoxide (Ta₂O₅), andmixtures thereof. Preferably, the high-index dielectric material forsuch filters is also UV-absorbing, i.e., absorbing in the near-UVspectral region. For example, a high-index dielectric material includingor consisting of TiO₂ and/or Nb₂O₅ may provide enhanced UV blocking,i.e., lower out-of-band transmittance in the near-UV spectral region.Preferably, the high-index dielectric material has a refractive indexgreater than about 2.0 at 550 nm, more preferably, greater than about2.35 at 550 nm. A higher refractive index is usually desirable. However,the transparent high-index dielectric materials that are currentlyavailable, generally, have refractive indices less than about 2.7 at 550nm.

For filters with a passband in the UV spectral region, the dielectriclayers are, typically, each composed of an intermediate-index dielectricmaterial having a refractive index between about 1.4 and 1.65 at 300 nmor, preferably, of a high-index dielectric material having a refractiveindex greater than about 1.65 at 300 nm, more preferably, greater thanabout 2.2 at 300 nm that is transparent in the UV spectral region.Suitable examples of intermediate-index and high-index dielectricmaterials for filters with a passband in the UV spectral region includeTa₂O₅, hafnium dioxide (HfO₂), aluminum trioxide (Al₂O₃), silicondioxide (SiO₂), scandium trioxide Sc₂O₃, yttrium trioxide (Y₂O₃), ZrO₂,magnesium dioxide (MgO2), magnesium difluoride (MgF₂), other fluorides,and mixtures thereof. For example, Ta₂O₅ may be used as a high-indexdielectric material for passbands centered at wavelengths above about340 nm, and HfO₂ may be used as a high-index dielectric material forpassbands centered at wavelengths below about 400 nm.

Generally, but not necessarily, the dielectric layers are composed ofthe same dielectric material, but have different thicknesses. Typically,the dielectric layers each have a physical thickness between about 20 nmand about 300 nm. Preferably, the top dielectric layer has a physicalthickness of greater than about 40 nm, more preferably, greater thanabout 100 nm, to enable the top dielectric layer to serve as aprotective layer for the metal layers below. The physical thickness ofeach dielectric layer is selected to correspond with a quarter waveoptical thickness (QWOT) required by an optical design. The QWOT isdefined as 4nt, where n is the refractive index of the dielectricmaterial and t is the physical thickness. Typically, the dielectriclayers each have a QWOT between about 200 nm and about 2400 nm.

The optional corrosion-suppressing layers are each composed of acorrosion-suppressing material. Typically, the corrosion-suppressinglayers are composed of a corrosion-suppressing dielectric material.Examples of suitable corrosion-suppressing dielectric materials includesilicon nitride (Si₃N₄), TiO₂, Nb₂O₅, zinc oxide (ZnO), and mixturesthereof. Preferably, the corrosion-suppressing dielectric material is acompound, e.g., a nitride or an oxide, of a metal having a highergalvanic potential than the metal or alloy of the metal layers.

In some instances, the corrosion-suppressing layers below the metallayers are composed of ZnO, whereas the corrosion-suppressing layersabove the metal layers include a very thin layer, e.g., having athickness of less than 1 nm, composed of zinc, and a thin layer composedof ZnO. The zinc layers are deposited on the metal layers, and thenpost-oxidized to prevent optical absorption. The ZnO layers below andabove the metal layers are, typically, deposited by reactive sputtering.Advantageously, depositing the zinc layers on the metal layers beforedepositing the ZnO layers prevents the metal layers from being exposedto the activated, ionized oxygen species that are produced duringreactive sputtering. The zinc layers preferentially absorb oxygen,suppressing the oxidation of the metal layers.

The corrosion-suppressing layers are, generally, suitably thin tosubstantially avoid contributing to the optical design of the opticalfilter, especially when they are absorbing in the visible spectralregion. Typically, the corrosion-suppressing layers each have a physicalthickness between about 0.1 nm and about 10 nm, preferably, betweenabout 1 nm and about 5 nm. Further details of suitablecorrosion-suppressing layers are disclosed in U.S. Pat. No. 7,133,197.

The optional protective coating is, typically, composed of a dielectricmaterial. The protective coating may be composed of the same dielectricmaterials and may have the same range of thicknesses as the dielectriclayers. Often, the protective coating is composed of the same dielectricmaterial as the top dielectric layer and has a thickness that is aportion of the design thickness, i.e., the thickness required by theoptical design, of the top dielectric layer. In other words, the topdielectric layer of the optical design is split between a dielectriclayer and a dielectric protective coating. Alternatively, the protectivecoating may be composed of an organic material, e.g., epoxy.

With reference to FIG. 3 , the optical filter 300, typically, has afilter height h, i.e., a height of the central portion of the opticalfilter 300 from the substrate 310, of less than 1 μm, preferably, ofless than 0.6 μm. It should be noted that the filter height, generally,corresponds to the thickness of the deposited coating referred toheretofore. When used in a image sensor, the optical filter 300,typically, has a filter width w, i.e., a width of the central portion ofthe optical filter 300, of less than 2 μm, preferably, of less than 1μm. Advantageously, the relatively small filter height allows a smallerfilter spacing when a plurality of optical filters 300 are formed by alift-off process. Typically, the optical filters 300 in an image sensorhave a filter spacing d, i.e., a spacing between the central portions ofnearest optical filters 300, of less than 2 μm, preferably, of less than1 μm. When used in other sensor devices with larger pixel sizes, thefilter width may be from about 50 μm to about 100 μm.

The optical filter is a metal-dielectric bandpass filter, i.e., aninduced transmission filter, having a high in-band transmittance and alow out-of-band transmittance. In some embodiments, the optical filteris a color filter having a relatively narrow color passband in thevisible spectral region. For example, the optical filter may be a red,green, blue, cyan, yellow, or magenta filter. In other embodiments, theoptical filter is a photopic filter having a photopic passband, i.e., apassband matching the photopic luminosity efficiency function thatmimics the spectral response of the human eye to relatively brightlight, in the visible spectral region. In yet other embodiments, theoptical filter is an IR-blocking filter having a relatively broadpassband in the visible spectral region.

In such embodiments, the optical filter, typically, has a maximumin-band transmittance of greater than about 50%, an average out-of-bandtransmittance of less than about 2% between about 300 nm and about 400nm, i.e., in the near-UV spectral region, and an average out-of-bandtransmittance of less than about 0.3% between about 750 nm and about1100 nm, i.e., in the infrared (IR) spectral region. In contrast,conventional all-dielectric color and photopic filters are not,typically, inherently IR-blocking. Generally, in such embodiments, theoptical filter also has a low angle shift, i.e., center-wavelength shiftwith change in incidence angle from 0°. Typically, the optical filterhas an angle shift at an incidence angle of 60° of less than about 5% orabout 30 nm in magnitude for an optical filter centered at 600 nm. Incontrast, conventional all-dielectric color and photopic filters are,typically, very angle-sensitive.

Optical designs, i.e., layer numbers, materials, and thicknesses, forexemplary red, green, and blue filters, i.e., an exemplary RGB filterset, are tabulated in FIGS. 4A, 4B, and 4C, respectively. An opticaldesign for an exemplary photopic filter is tabulated in FIG. 4D. Thelayers of each optical design are numbered starting from the first orbottom layer deposited on the substrate.

The metal layers are each composed of silver, and have physicalthicknesses between about 13 nm and about 34 nm. The dielectric layersare each composed of a high-index dielectric material (H), and haveQWOTs between about 240 nm and about 2090 nm. For example, thehigh-index dielectric material may be a mixture of Nb₂O₅ and TiO₂ havinga refractive index of about 2.43 at 550 nm. The corrosion-suppressinglayers are each composed of ZnO and each have a physical thickness ofabout 2 nm.

When the high-index dielectric material has a refractive index of about2.43 at 550 nm, the filter height of the red filter is 606 nm, that ofthe green filter is 531 nm, that of the blue filter is 252 nm, and thatof the photopic filter is 522 nm. These filter heights are considerablysmaller than those of conventional all-dielectric color and photopicfilters.

Transmission spectra 570, 571, and 572 for the exemplary red, green, andblue filters, respectively, are plotted in FIGS. 5A and 5B. Thetransmission spectrum 570 for the exemplary red filter includes a redpassband centered at about 620 nm, the transmission spectrum 571 for theexemplary green filter includes a green passband centered at about 530nm, and the transmission spectrum 572 for the exemplary blue filterincludes a blue passband centered at about 445 nm.

Transmission spectra 573 (0°) and 574 (60°) for the exemplary photopicfilter at incidence angles of 0° to 60° are plotted in FIG. 5C. Thetransmission spectrum 573 for the exemplary photopic filter at anincidence angle of 0° includes a photopic passband centered at about 555nm. In the transmission spectrum 574 for the exemplary photopic filterat an incidence angle of 60°, the photopic passband is centered at about520 nm. In other words, the angle shift of the exemplary photopic filterat an incidence angle of 60° is about −25 nm. Advantageously, the angleshift of the exemplary photopic filter is considerably smaller than theangle shift of a conventional all-dielectric photopic filter.

The exemplary color and photopic filters each have a maximum in-bandtransmittance of greater than about 60%. Advantageously, the exemplarycolor and photopic filters provide improved IR blocking relative toconventional dye-based and all-dielectric color and photopic filters,reducing noise caused by IR leaking. Specifically, the exemplary colorand photopic filters each have an average out-of-band transmittance ofless than about 0.3% between about 750 nm and about 1100 nm, i.e., inthe IR spectral region. The exemplary color and photopic filters,particularly the exemplary red filter, also provide improved UV blockingrelative to some conventional metal-dielectric color filters, reducingnoise caused by UV leaking. Specifically, the exemplary color andphotopic filters each have an average out-of-band transmittance of lessthan about 2% between about 300 nm and about 400 nm, i.e., in thenear-UV spectral region.

A color gamut 680 for the exemplary RGB filter set is plotted on a CIExy chromaticity diagram in FIG. 6A, along with a color gamut 681 for aconventional dye-based RGB filter set for comparison. Advantageously,the color gamut 680 of the exemplary RGB filter set is considerablylarger than the color gamut 681 of the conventional dye-based RGB filterset.

A color trajectory 682 for the exemplary red filter at incidence anglesof 0° to 60° is plotted on a CIE xy chromaticity diagram in FIG. 6B,along with a color trajectory 683 for a conventional all-dielectric redfilter at incidence angles of 0° to 60°. A color trajectory 684 for theexemplary photopic filter at incidence angles of 0° to 60° is plotted ona CIE xy chromaticity diagram in FIG. 6C. Advantageously, the angleshift of the exemplary red and photopic filters is considerably smallerthan the angle shift of conventional all-dielectric red and photopicfilters.

In some embodiments, the optical filter is a UV filter having arelatively narrow passband in the UV spectral region, e.g., betweenabout 180 nm and about 420 nm. For example, the optical filter may be anultraviolet-A (UVA) or ultraviolet-B (UVB) filter. In such embodiments,the optical filter typically, has a maximum in-band transmittance ofgreater than about 5%, preferably, greater than about 15%, and anaverage out-of-band transmittance of less than about 0.3% between about420 nm and about 1100 nm, i.e., in the visible and IR spectral regions.In contrast, conventional all-dielectric UV filters are not, typically,inherently IR-blocking. Generally, in such embodiments, the opticalfilter also has a low angle shift, i.e., center-wavelength shift withchange in incidence angle from 0°. Typically, the optical filter has anangle shift at an incidence angle of 60° of less than about 5% or about15 nm in magnitude for an optical filter centered at 300 nm. Incontrast, conventional all-dielectric UV filters are, typically, veryangle-sensitive.

Optical designs, i.e., layer numbers, materials, and thicknesses, forexemplary UVA, UVB, and 220-nm-centered filters are summarized in FIG.12 . The metal layers are each composed of aluminum, and have physicalthicknesses between about 10 nm and about 20 nm. The dielectric layersare each composed of a high-index dielectric material, namely, Ta₂O₅ forthe UVA filter, and HfO₂ for the UVB and 220-nm-centered filters, andhave physical thicknesses between about 40 nm and about 60 nm. Theexemplary UV filters do not include corrosion-suppressing layers, as theadditional protection they provide is not usually necessary when themetal layers are composed of aluminum.

The filter height of the UVA filter is 350 nm, that of the UVB filter is398 nm, and that of the 220-nm-centered filter is 277 nm. These filterheights are considerably smaller than those of conventionalall-dielectric UV filters.

Transmission spectra 1370 (0°) and 1371 (60°) for the exemplary UVAfilter at incidence angles of 0° to 60° are plotted in FIG. 13A,transmission spectra 1372 (0°) and 1373 (60°) for the exemplary UVBfilter at incidence angles of 0° to 60° are plotted in FIG. 13B, andtransmission spectra 1374 (0°) and 1375 (60°) for the exemplary220-nm-centered filter at incidence angles of 0° to 60° are plotted inFIG. 13C. The transmission spectrum 1370 for the exemplary UVA filter atan incidence angle of 0° includes a UVA passband centered at about 355nm, the transmission spectrum 1372 for the exemplary UVB filter at anincidence angle of 0° includes a UVB passband centered at about 295 nm,and the transmission spectrum 1374 for the 220-nm-centered filter at anincidence angle of 0° includes a passband centered at about 220 nm. Theangle shift of the exemplary UV filters at an incidence angle of 60° isless than about 15 nm in magnitude. Advantageously, the angle shift ofthe exemplary UV filters is considerably smaller than the angle shift ofconventional all-dielectric UV filters.

The exemplary UV filters each have a maximum in-band transmittance ofgreater than about 10%. In particular, the UVA and UVB filters each havea maximum in-band transmittance of greater than about 20%.Advantageously, the exemplary UV filters provide improved IR blockingrelative to conventional all-dielectric UV filters, reducing noisecaused by IR leaking. Specifically, the exemplary UV filters each havean average out-of-band transmittance of less than about 0.3% betweenabout 420 nm and about 1100 nm, i.e., in the visible and IR spectralregions.

The optical filter of the present invention is particularly useful whenincluded as part of a sensor device or other active device. The sensordevice may be any type of sensor device including one or more sensorelements, in addition to one or more optical filters according to thepresent invention. In some instances, the sensor device may also includeone or more conventional optical filters. For example, the sensor devicemay be an image sensor, an ambient light sensor, a proximity sensor, anhue sensor, a UV sensor, or a combination thereof. The one or moresensor elements may be any type of conventional sensor elements.Typically, the one or more sensor elements are photodetectors, such asphotodiodes, charge-coupled device (CCD) sensor elements, complementarymetal-oxide semiconductor (CMOS) sensor elements, silicon detectors, orspecial UV-sensitive detectors. The one or more sensor elements may befront- or back-illuminated. The sensor elements may be formed of anytypical sensor material, such as silicon, indium gallium arsenide(In_(1-x)Ga_(x)As), gallium arsenide (GaAs), germanium, lead sulfide(PbS), or gallium nitride (GaN).

The one or more optical filters are disposed over the one or more sensorelements, so that the one or more optical filters filter light providedto the one or more sensor elements. Typically, each optical filter isdisposed over one sensor element. In other words, each pixel of thesensor device, typically, includes one optical filter and one sensorelement. Preferably, the one or more optical filters are disposeddirectly on the one or more sensor elements, e.g., on a passivationlayer of the one or more sensor elements. For example, the one or moreoptical filters may be formed on the one or more sensor elements by alift-off process. However, in some instances, there may be one or morecoatings disposed between the one or more optical filters and the one ormore sensor elements. In some instances, the one or more optical filtersmay be integrated with the one or more sensor elements.

In some embodiments, the sensor device includes a single sensor elementand a single optical filter according to the present invention disposedover the sensor element. With reference to FIG. 7 , a first embodimentof the sensor device 790 includes a sensor element 711 and an opticalfilter 700 disposed on the sensor element 711. For example, the sensordevice 790 may be an ambient light sensor, the sensor element 711 may bea photodiode, and the optical filter 700 may be a photopic filter, suchas the exemplary photopic filter of FIG. 4D, or an IR-blocking filter.For another example, the sensor device 790 may be a UV sensor, thesensor element 711 may be a photodiode, and the optical filter 700 maybe a UV filter, such as the exemplary UVA, UVB, or 220-nm-centred filterof FIG. 12 .

In an exemplary embodiment of an ambient light sensor, a photopic filteraccording to the present invention is integrated with a photodiode. Thephotopic filter is disposed on the photodiode, typically, on aplanarized passivation layer, e.g., composed of Si₃N₄, of thephotodiode. An optional protective coating or encapsulation layer, e.g.,composed of epoxy, may be disposed over the photopic filter and thephotodiode. The optical design of the photopic filter is optimized bytaking the passivation layer and, when present, the encapsulation layerinto account.

Transmission spectra 1470 (0°) and 1471 (60°) for an exemplary photopicfilter optimized for integration with a photodiode at incidence anglesof 0° to 60° are plotted in FIG. 14 , along with a normalized photopicresponse curve 1472. The transmission spectra 1470 and 1471 are matchedto a Si₃N₄ passivation layer and an epoxy encapsulation layer. Thetransmission spectrum 1470 for the exemplary photopic filter at anincidence angle of 0° includes a photopic passband centered at about 555nm. The transmission spectra 1470 for the exemplary photopic filterfollow the normalized photopic response curve 1472 reasonably well atincidence angles of 0° to 40°. Moreover, the exemplary photopic filterblocks both UV and IR light at incidence angles of 0° to 60°, and has alow angle shift. Advantageously, the exemplary photopic filter is alsoenvironmentally durable, e.g., at a temperature of 125° C. and arelative humidity of 100% for 96 hours.

In other embodiments, the sensor device includes a plurality of sensorelements, and a plurality of optical filters according to the presentinvention disposed over the plurality of sensor elements. Typically, thesensor elements are disposed in an array. In other words, the sensorelements form a sensor array, such as a photodiode array, a CCD array, aCMOS array, or any other type of conventional sensor array. Alsotypically, the optical filters are disposed in an array. In other words,the optical filters form an optical filter array, such as a color filterarray (CFA). Preferably, the sensor array and the optical filter arrayare corresponding two-dimensional arrays, i.e., mosaics. For example,the arrays may be rectangular arrays having rows and columns.

Often, in such embodiments, the optical filters are substantiallyseparate from one another. In other words, the peripheries of theoptical filters are not usually in contact with one another. However, insome instances, the dielectric layers of the optical filters mayunintentionally touch, while the metal layers, particularly, the taperededges, remain separate from one another.

Typically, the plurality of optical filters includes different types ofoptical filters having different passbands from one another. Forexample, the plurality of optical filters may include color filters,such as red, green, blue, cyan, yellow, and/or magenta filters, photopicfilters, IR-blocking filters, UV filters, or a combination thereof. Insome embodiments, the plurality of optical filters includes differenttypes of color filters, forming a CFA. For example, the plurality ofoptical filters may include red, green, and blue filters, such as theexemplary red, green, and blue filters of FIGS. 4A to 4C, forming an RGBfilter array, such as a Bayer filter array. For another example, theplurality of optical filters may include cyan, magenta, and yellowfilters, forming a CMY filter array.

Advantageously, the different types of optical filters may havedifferent numbers of metal layers and/or different thicknesses of themetal layers from one another. In some embodiments, at least two of thedifferent types of optical filters include different numbers of metallayers from one another. In the same or other embodiments, at least twoof the different types of optical filters have different metal-layerthicknesses from one another. For example, the exemplary blue filter ofFIG. 4C has a different number of metal layers from the exemplary redand green filters of FIGS. 4A and 4B. Moreover, all of the exemplaryred, green, and blue filters of FIGS. 4A to 4C have differentmetal-layer thicknesses from one another.

With reference to FIG. 8 , a second embodiment of the sensor device 890includes a plurality of sensor elements 811 and a plurality of opticalfilters 800 and 804 disposed on the plurality of sensor elements 811.The plurality of optical filters 800 and 804 includes a first type ofoptical filter 800 having a first passband, and a second type of opticalfilter 804 having a second passband, different from the first passband.For example, the sensor device 890 may be an image sensor, the pluralityof sensor elements 811 may form a CCD array, and the plurality ofoptical filters 800 and 804 may form a Bayer filter array, of which onlya portion of one row is illustrated. The first type of optical filter800 may be a green filter, such as the exemplary green filter of FIG.4B, and the second type of optical filter 804 may be a red filter, suchas the exemplary red filter of FIG. 4A, or a blue filter, such as theexemplary blue filter of FIG. 4C.

Any of the embodiments of the sensor device described heretofore may becombined with one or more additional optical filters that are moreenvironmentally durable and one or more additional sensor elements.

Accordingly, in some embodiments, the sensor device includes one or moresecond optical filters disposed over one or more second sensor elements,in addition to one or more first optical filters according to thepresent invention disposed over one or more first sensor elements. Theone or more second optical filters are more environmentally durable thanthe one or more first optical filters. For example, the one or morefirst optical filters may be silver-dielectric optical filters accordingto the present invention, in which the metal layers are composed ofsilver or a silver alloy. The second one or more second optical filtersmay be an aluminum-dielectric optical filters according to the presentinvention, in which the metal layers are composed of aluminum.Alternatively, the one or more second optical filters may beconventional optical filters, such as all-dielectric,silicon-dielectric, or hydrogenated-silicon-dielectric optical filters.

In such embodiments, the one or more second optical filters partiallyoverlap with the one or more first optical filters, such that the one ormore second optical filters that are more environmentally durableprotectively cover the peripheries of the one or more first opticalfilters that are less environmentally durable. Advantageously, thisoverlapping layout provides the one or more first optical filters,particularly, the tapered edges of the metal layers, with additionalprotection from environmental degradation such as corrosion. Owing tothe small slope of the filter sides and the small filter height of theone or more first optical filters, the one or more second opticalfilters conform when deposited on the sloped sides at the peripheries ofthe one or more first optical filters and the substrate, providingcontinuous layers in the one or more second optical filters.

The one or more second optical filters extend over the sloped sides atthe peripheries of the one or more first optical filters, including thetapered edges of the metal layers, preferably, along the entireperipheries of the one or more first optical filters. Preferably, theone or more second optical filters completely cover the sloped sides atthe peripheries of the one or more first optical filters. However, theone or more second optical filters do not cover or obstruct the one ormore first sensor elements.

Typically, the one or more first optical filters and the one or moresecond optical filters have different passbands from one another. Forexample, the one or more first optical filters may be color filters,such as red, green, blue, cyan, yellow, or magenta filters, photopicfilters, IR-blocking filters, or a combination thereof. In particular,the one or more first optical filters may be silver-dielectric colorfilters, such as the exemplary red, green, and/or blue filters of FIGS.4A to 4C, silver-dielectric photopic filters, such as the exemplaryphotopic filter of FIG. 4D, or silver-dielectric IR-blocking filters.

The one or more second optical filters may, for example, be UV filtersor near-IR filters, or a combination thereof. In particular, the one ormore second optical filters may be aluminum-dielectric UV filters, suchas the exemplary UVA, UVB, and/or 220-nm-centered filters of FIG. 12 ,or all-dielectric UV filters. Alternatively, the one or more secondoptical filters may be silicon-dielectric orhydrogenated-silicon-dielectric near-IR filters, such as the opticalfilters described in U.S. Patent Application Publication No.2014/0014838 to Hendrix, et al., published on Jan. 16, 2014, which isincorporated herein by reference, or all-dielectric near-IR filters.

Typically, the sensor device, in such embodiments, is multifunctionaland combines different types of optical sensors having differentfunctions, mainly determined by the passbands of the one or more firstoptical filters and the one or more second optical filters. The one ormore first optical filters and the one or more first sensor elementsform a first type of optical sensor, and the one or more second opticalfilters and the one or more second sensor elements form a second type ofoptical sensor. For example, the first type of optical sensor may be anambient light sensor including a photopic filter or an IR-blockingfilter, a hue sensor including one or more different types of colorfilters, or an image sensor including a plurality of different types ofcolor filters. The second type of optical sensor may, for example, be aUV sensor including a UV filter, or a proximity sensor including anear-IR filter.

With reference to FIG. 15 , a third embodiment of a sensor device 1590includes a first sensor element 1511 and a first optical filter 1500according to the present invention disposed on the first sensor element1511, forming a first type of optical sensor. The sensor device 1590further includes a second sensor element 1512 and a second opticalfilter 1505 that is more environmentally durable disposed on the secondsensor element 1512, forming a second type of optical sensor.

For example, the first type of optical sensor may be an ambient lightsensor, and the first optical filter 1500 may be a silver-dielectricphotopic filter, such as the exemplary photopic filter of FIG. 4D, or asilver-dielectric IR-blocking filter. The second type of optical sensormay, for example, be a UV sensor, and the second optical filter 1505 maybe an aluminum-dielectric UV filter, such as the exemplary UVA, UVB, or220-nm-centered filter of FIG. 12 , or an all-dielectric UV filter.Alternatively, the second type of optical sensor may be a proximitysensor, and the second optical filter 1505 may be a near-IR filter, suchas an all-dielectric, silicon-dielectric, orhydrogenated-silicon-dielectric near-IR filter. The first sensor element1511 and the second sensor element 1512 may be photodiodes.

With particular reference to FIG. 15A, the second optical filter 1505extends over the sloped sides of the first optical filter 1500 along theentire periphery of the first optical filter 1500. Thereby, the secondoptical filter 1505 protectively covers the periphery of the firstoptical filter 1500, including the tapered edges of the metal layers.

With particular reference to FIGS. 15B and 15C, the first optical filter1500 covers and filters light provided to the first sensor element 1511.The second optical filter 1505 covers and filters light provided to thesecond sensor element 1512, and surrounds, but does not cover, the firstsensor element 1511. In the layout illustrated in FIG. 15B, the firstsensor element 1511 and the second sensor element 1512 are disposed in arow between rows of bond pads 1513. In an alternative layout illustratedin FIG. 15C, the second sensor element 1512 is annular and surrounds thefirst sensor element 1511.

With reference to FIG. 16 , a fourth embodiment of a sensor device 1690includes a plurality of first sensor elements 1611 and a plurality offirst optical filters 1600, 1604, and 1606 according to the presentinvention disposed on the plurality of first sensor elements 1611,forming a first type of optical sensor. The sensor device 1690 furtherincludes a second sensor element 1612 and a second optical filter 1605disposed over the second sensor element 1612, forming a second type ofoptical sensor.

For example, the first type of optical sensor may be an image sensor ora hue sensor, and the plurality of first optical filters 1600, 1604, and1606 may be different types of color filters, such as the exemplarysilver-dielectric red, green, and blue filters of FIGS. 4A to 4C. Thesecond type of optical sensor may, for example, be a UV sensor, and thesecond optical filter 1605 may be a UV filter, such as the exemplaryaluminum-dielectric UVA, UVB, or 220-nm-centered filter of FIG. 12 .Alternatively, the second type of optical sensor may be a proximitysensor, and the second optical filter 1605 may be a near-IR filter, suchas an all-dielectric, silicon-dielectric, orhydrogenated-silicon-dielectric near-IR filter. The plurality of firstsensor elements 1611 and the second sensor element 1612 may form aphotodiode array.

Of course, numerous other embodiments may be envisaged without departingfrom the spirit and scope of the invention.

We claim:
 1. A method comprising: applying a photoresist layer onto asubstrate; forming, in the photoresist layer surrounding a region of thesubstrate, an overhang by patterning the photoresist layer in a mannerthat uncovers the region; and lifting the photoresist layer in a mannerthat provides a clean lift-off of the photoresist layer without breakinga coating that covers the overhang.
 2. The method of claim 1, whereinthe photoresist layer comprises a bilayer structure.
 3. The method ofclaim 1, wherein the photoresist layer includes a top layer that isphotosensitive.
 4. The method of claim 1, wherein the photoresist layerincludes a top layer that is patternable by selective exposure toultraviolet light.
 5. The method of claim 1, wherein the photoresistlayer includes a bottom layer that is not photosensitive and acts as arelease layer.
 6. The method of claim 1, wherein the region is a filterregion.
 7. The method of claim 1, wherein forming the overhangcomprises: chemically modifying a top portion of the photoresist layerfor the top portion to develop more slowly than a bottom portion of thephotoresist layer.
 8. The method of claim 1, wherein the overhang isgreater than 2 μm.
 9. The method of claim 1, wherein the coating is amultilayer stack coating.
 10. The method of claim 1, wherein a thicknessof the coating is less than about 70% of a thickness of a bottom layerof the photoresist layer.
 11. The method of claim 1, wherein a thicknessof a bottom layer of the photoresist layer is about 800 nm.
 12. Themethod of claim 1, wherein a thickness of the coating is about 500 nm.13. The method of claim 1, wherein sides of an optical filter under theoverhang are sloped at an angle of about 10 degrees.
 14. An opticalfilter comprising: a photoresist layer, the photoresist layer includinga top layer and a bottom layer; an overhang; and a coating that coversthe top layer and the overhang, a thickness of the coating beingconfigured to ensure a clean lift-off the photoresist layer withoutbreaking the coating.
 15. The optical filter of claim 14, wherein thetop layer is photosensitive and is patternable by selective exposure toultraviolet light.
 16. The optical filter of claim 14, wherein thebottom layer is not photosensitive and acts as a release layer.
 17. Theoptical filter of claim 14, wherein the thickness of the coating is lessthan about 70% of a thickness of the bottom layer.
 18. An optical filtercomprising: a photoresist layer; and an overhang that is greater thanabout 2 μm; and a coating that covers the overhang, a thickness of thecoating being configured to ensure a clean lift-off the photoresistlayer without breaking the coating.
 19. The optical filter of claim 18,wherein a side of the optical filter under the overhang is sloped at anangle of about ten degrees.
 20. The optical filter of claim 18, whereinthe photoresist layer includes a release layer, wherein the thickness ofthe coating is about 500 nm, and wherein the thickness of the coating isless than about 70% of a thickness of the release layer.